This application relates generally to the field of torque angle wrenches and, more particularly, to a torque-angle wrench including a ratchet drive.
A torque wrench measures the torque applied to a fastener as an indication of the joining force or load. However, torque is considerably influenced by friction forces, the condition of the fasteners, the amount, if any, of lubrication present, as well as by other factors. Accordingly, the reliability of a torque measurement as an indication of desired load is significantly variable. For this reason, a torque-angle fastener installation process, rather than torque measurement alone, is recommended in situations where tightening to recommended specifications is critical.
In a torque-angle fastener installation, a fastener is first tightened to a desired torque using a torque wrench, and is then rotated through a predetermined additional angle of rotation. There are various wrenching tools available which meter angular rotation. Such a wrench, which utilizes a piezoelectric gyroscopic element to measure rotation of the fastener during a torquing operation, is disclosed in U.S. Pat. No. 5,589,644 which discloses a wrench with a fixed drive head, and the disclosure of which is incorporated herein by reference. In the use of that wrench, angle measurement is initiated at a predetermined torque level, the torque-measuring and angle measuring phases of the operation all occurring during a single continuous stroke of the wrench.
However, in many applications, such as where there is limited space for rotational movement of the wrench, the use of a ratchet drive on an angle-measuring wrench is desired. With such a ratchet drive, as is well known, the wrench is oscillated back and forth between torque-applying and ratcheting directions. The use of such a ratchet drive introduces error in the angle measurement because of lost motion between ratchet mechanism teeth. For example, a ratchet mechanism may feature a ratchet gear with 36 teeth. Thus, when rotating the wrench in the ratcheting direction, the angular distance between teeth is 10 degrees. Accordingly, the amount of angular rotation “lost motion” of the wrench in the torquing direction could be anywhere between zero and ten degrees before torque is actually applied to the fastener.
Similarly, any looseness between the wrench and the fastener, such as through the use of a socket tool, would introduce additional lost motion. Also, the use of common tools, such as extensions and/or universal drives, would add to the stack-up of lost motion before actually applying torque to the fastener.
Accordingly, in order to accurately, use a ratchet drive with an angle-measuring wrench, it is necessary to account for or ignore the lost motion that may be introduced each time the wrench is rotated in the ratcheting direction.